XRT7250 datasheet(351/463 Pages) EXAR

351 / 463 page

XRT7250

áç

DS3/E3 FRAMER IC

REV. 1.1.1

332

6.0

E3/ITU-T G.832 OPERATION OF THE

XRT7250

Configuring the XRT7250 to Operate in the E3,

ITU-T G.832 Mode

The XRT7250 can be configured to operate in the E3/

ITU-T G.832 Mode by writing a “0” into bit-field 6 and

a “1” into bit-field 2, within the Framer Operating

Mode register, as illustrated below.

Prior to describing the functional blocks within the

Transmit and Receive Sections of the XRT7250, it is

important to describe the E3, ITU-T G.832 framing

format.

6.1

DESCRIPTION OF THE E3, ITU-T G.832 FRAMES

AND

ASSOCIATED OVERHEAD BYTES

The role of the various overhead bytes are best de-

scribed by discussing the E3, ITU-T G.832 Frame

Format as a whole. The E3, ITU-T G.832 Frame con-

tains 537 bytes, of which 7 bytes are overhead and

the remaining 530 bytes are payload bytes.

These 537 octets are arranged in 9 rows of 60 col-

umns each, except for the last three rows which con-

tain only 59 columns. The frame repetition rate for

this type of E3 frame is 8000 times per second, there-

by resulting in the standard E3 bit rate of 34.368

Mbps. Figure 154 presents an illustration of the E3,

ITU-T G.832 Frame Format.

6.1.1

Definition of the Overhead Bytes

The seven (7) overhead bytes are shown in

Figure 154, as FA1, FA2, EM, TR, MA, NR and GC.

Each of these Overhead Bytes are further defined be-

low.

FRAMER OPERATING MODE REGISTER (ADDRESS = 0X00)

BIT 7

BIT 6BIT 5BIT 4BIT 3

BIT2BIT 1BIT 0

Local Loopback

DS3/E3*

Internal

LOS Enable

RESET

Interrupt

Enable Reset

Frame Format

TimRefSel[1:0]

R/W

FIGURE 154. ILLUSTRATION OF THE E3, ITU-T G.832 FRAMING FORMAT.

FA1

FA2

1 Byte

59 Bytes

60 Columns

9 Rows

530 Octet Payload

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